4-Methyl-2-(2-methyl-1-propenyl)tetrahydro-2H-pyran (hereinafter sometimes referred to simply as rose oxide) is a compound which was found from Bulgarian rose oil in 1959 and occurs in essential oils of sweetbrier, geranium, lily, pelargonium, Fatsia japonica, gardenia, peppermint, etc., flavors of apricot, tomato, etc., and secretions of insects such as the musk long-horned beetle, etc.
Rose oxide has geometrical isomers and optical isomers and (4R)-cis- and trans-4-methyl-2-(2-methyl-1-propenyl)tetrahydro-2H-pyrans are found in natural plants such as roses and geraniums.
For the chemical synthesis of rose oxide, there have been known a method using .beta.-citronellol as the starting material and another method using dihydropyrans as the starting materials.
In general, rose oxide has a refreshing, floral and green note. However, the fragrance delicately varies from isomer to isomer. That is to say, cis-rose oxide has a green note just like a geranium and peppermint, while trans-rose oxide has a somewhat intense fragrance compared with the cis-isomer U.S. Pat. No. 3,161,657(1964)!. Further, it is described that (4R)-rose oxide has a sweet and floral fragrance with an intense green note while (4S)-rose oxide has a fragrance with a somewhat spicy note Perfume and Flavor Chemicals II, 2809 (1969)!. It is also reported that rose oxide is usable in compounding various perfumes including rose and geranium based perfumes, since the addition of rose oxide in an amount of 0.05 to 0.5% imparts a light and floral top note to the perfumes Koryo (Perfume), 178, 114 (June, 1993)!. However, the details are not stated relating to the all four individual optical isomers Olfaction and Taste, 4, 156 (1972)!.
It is reported that 4-methyl-2-(2-methylpropyl)tetrahydro-2H-pyran (hereinafter sometimes referred to as dihydrorose oxide) is synthesized from 3-methylbuten-3-ol-1 and 3-methylbutanal, and has a fragrance similar to that of rose oxide and is more stable to heat, acids and light than rose oxide, though nothing is stated relating to its optical isomers Perfumer & Flavarist, 11, Jun./Jul. 29 (1986)!.
With the recent diversification of perfumes and cosmetics, it has been required to develop a novel perfume material which is excellent in various characteristics (safety, stability, preference, freshness, natural feel, etc.) and has a good and intense fragrance. Accordingly, the present invention aims at providing a perfume composition containing a rose oxide which is capable of imparting a fresh, refreshing and rose green feel to a fragrance, and a method for improving a fragrance by which such a fragrance can be imparted.